It is known that one can use for the low-pressure polymerization of olefins catalytic systems comprising a halogenated derivative of a transition metal and an organometallic compound.
British Pat. No. 1,140,649 shows that it is also known that one can use catalysts in which the halogenated derivative of the transition metal is fixed onto a solid support. This solid support is an oxygenated compound of a divalent metal. By reaction between the halogenated derivative and the solid support complexes are formed comprising halogen, the divalent metal and the transition metal. It is observed that there is a surface halogenation of the solid support, but that this halogenation is weak. Generally speaking, the total quantity of halogen present is less than 0.05 atoms of halogen per atom of divalent metal. Such catalyst systems while suitable are still lacking in the activity desired.